In recent years, temperature control of oil that is used to lubricate internal combustion engines has been becoming increasingly important. This is because the temperature and the viscosity of oil are correlated with each other, and the oil viscosity needs to be maintained in a fixed range in order to maintain a constant oil film thickness. Moreover, oil that is discharged from a lubrication path of an internal combustion engine in use usually has a higher temperature than an appropriate temperature range. Thus, it has been considered to cool the oil to a temperature within the appropriate temperature range before it is supplied again to the lubrication path (see, for example, Patent Document 1 and Patent Document 2).
Patent Document 1: Japanese Patent Application Publication No. H10-176515
Patent Document 2: Japanese Patent Application Publication No. 2000-176204